Infra-red detector comprising polymerized organic material



Get. 11, 1966 J. J. BRISSOT ETAL 3,278,783

INFRA-RED DETECTOR COMPRISING POLYMERIZED ORGANIC MATERIAL Filed March 5, 1964 INVENTORS JEAN JACQUES BRISSOT JEAN NICOLAS JEAN PER/LHOU AGENT Patented Oct. 11, 1366 3,278,783 INFRA-RED DETECTOR COMPRISING POLYM- ERIZED ORGANIC MATERIAL Jean Jacques Brissot, Paris, Jean Nicolas, St. Germain en Laye, and Jean Perilhou, Arnoux-Bourg la Reine, France, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Mar. 5, 1964, Ser. No. 349,714 Claims priority, application France, Mar. 15, 1963,

10 Claims. (or. 313-101) The invention relates to an electron tube for detecting infrared radiation provided with a target screen for this radiation, which screen comprises a thin layer of a material having a temperature-dependent electrical resistance, said layer being supported by a support and being provided with an electrode.

In an electron tube of the said kind the infrared radiation to be detected is converted into heat which changes the electrical resistance of the said temperature-sensitive layer to a greater or lesser extent, the said conversion being performed by absorption in the temperature-sensitive layer or in an adjoining layer, for example, in the said electrode. The said resistance variation, which when an infrared image is projected onto the target screen may be different in different areas, may be used to obtain electrical signals corresponding to the infrared image (image signal tube) or may be rendered visible by electro-optical means (image converter tube). In a known image signal tube of the said kind the thin temperature-sensitive layer consists of a thermistor material, for example, manganese oxide, and is adapted to be scanned by an electron beam. With respect to image conversion it is known to provide a target screen comprising a temperature-sensitive layer of conductive glass with a mosaic of minute photo-emissive islands, the photo-emission current of the islands, which is obtained by means of an auxiliary source of light and is controlled by the local resistance of the temperaturesensitive layer being directed onto a luminescent screen. As is known an image converter tube may alternatively be obtained by using in an electron tube a target screen which is provided with an electrode and the resistance of which may be changed by infrared radiation as an electron mirror for the electrons of an electron beam directed onto the said screen in a manner such that the reflected electrons produce, on a luminescent screen, an image corresponding to the infrared image on the target screen.

The usual thermistor materials have a limitation in that their specific electric resistivity is rather low; this also applies to many temperaturesensitive semi-conductors. This low resistivity is troublesome particularly in image signal tubes and can only be compensated for by additional steps such as subdivision of the layer of thermistor material, the use of a second electron gun producing a beam flooding the entire layer with electrons or intensive cooling of the target screen to temperatures far below C.

It is an object of the invention to provide an electron tube of the kind mentioned in the preamble, in which especially by the choice of the mate-rial of the thin layer such additional steps can be dispensed with so that the target screen construction of the tube may be simple and also during operation no or substantially no cooling of the target screen is required so that no special additional equipment is required.

According to the invention an electron tube of the kind mentioned in the preamble is characterized in that the thin -layer is in the form of a film or foil of a polymerized material having a low thermal conductivity and a specific electric resi-stively (p) between 10 ohm-cm. and 10 ohmcm. the relative resistance variation per C. i.e.

p AT

being at least 5% in a temperature range between .0 .C. and C.

In a favorable embodiment of the invention the temperature-sensitive layer is a foil of organic thermoplastic material, for example a foil of polyacrylonitrile, polyvinyl acetate or polyvinylcyanurate. However, the temperaturesensitive layer may also be a foil of a polymerized material of markedly inorganic nature, for example, a polyphosphonitrile chloride. According to the invention also a film or foil consisting of a polymerized material of semimetallic, semi-organic nature, such as polychelates or certain derivates of metals of sandwich sructure may be used as the temperature-sensitive layer in the target screen.

According to a further embodiment of the invention the electrode in contact with the thin temperature-sensitive layer consists of a thin layer of gold or silver deposited from the vapor phase, the arrangement being such that when gold is used this layer is translucently blue-green and when silver is used is translucently blue. These layers have a strong absorption in the wavelength range between 1 and 10 so that infrared radiation incident on the target screen is absorbed in such a layer. The heat generated thereby is readily transferred to the temperaturesensitive foil but the spreading of the heat in the direction of the plane of the layer is slight. The use of gold or silver for the above-mentioned purpose is of particular importance when the temperature-sensitive layer, which according to the invention comprises a film or foil of polymerized material, itself does not, or not completely, absorb infrared radiation. Alternatively, however, the thin temperature-sensitive layer may consist of a foil comprising a temperature-sensitive material not absorbing infrared radiation and a filler material absorbing infrared radiation.

The invention will now be described with reference to the accompanying drawing, in which:

FIGURE 1 is a diagrammatic sectional view of an image signal tube; and

FIGURE 2 is a sectional view, on an enlarged scale, of part of the target of the tube of FIGURE 1.

The image signal tube of FIGURE 1 shows strong similarity to a television camera tube of the vidicon type, in which a photo-conductive target provided on a transparent signal electrode is scanned by an electron beam of low-velocity electrons. The tube shown in FIGURE 1 has a cylindrical glass envelope 1 closed at one end by a window 2 of a material transmitting infrared radiation. The tube further contains a diagrammatically shown electron gun 3 and electrode system 4 terminated by a grid 5, the arrangement being similar to that used in a conventional vidicon. The tube 1 is surrounded by the conventional focusing and deflecting coils (not shown) for the electron beam 7 which is emitted from the cathode 6 of the electron gun 3 and scans a target screen 8 disposed immediately behind the window 2 and in front of the grid 5.

The target screen 8 is constituted by a foil 9 of a polymerized organic material, for example, polyacrylonitrile, which is about In thick and is supported along its edge by an annular support 10. This support 10 may be in the form of a glass ring ground flat. On the surface of the foil 9 remote from the electron gun 3 a thin conductive layer 11 constituting the signal electrode and extending to the support 10 is deposited from the vapor phase. The support 10 is supported by a metal ring 12 with which also the window 2 is joined to the envelope 1. Consequently the conductive layer 11 is electrically connected to the ring 12 and, during the operation of the tube, through this ring and a signal resistor to the positive terminal of a direct-voltage source 14 of for instance about 100 v. the negative terminal of which is connected to the cathode 6 of the electron gun 3. The conductive layer 11 acting as the signal electrode may be a thin layer of metal, for example, aluminum deposited from the vapor phase. However, the signal electrode 11 preferably is either a layer of gold deposited from the vapor phase and translucently blue-green or a layer of silver deposited from the vapor phase and translucently blue.

During the operation of the tube infrared radiation shown by arrows 15 in FIGURE 1 is projected through the window 2 onto the target screen 8, and by absorption in either the signal electrode 11 or the foil 9' or both is converted into heat. As a result the temperature of the foil 9 is locally raised to a greater or lesser extent and hence the electrical resistance of this foil, measured in the direction of thickness, is correspondingly reduced. When the foil 9 is scanned by the electron beam 7 the said local reduction of its resistance shows itself as a corresponding electric signal across the signal resistor 13. This conversion of the local variation in resistance of the foil 9 into an electrical signal across the resistor 13 is effected in the same Way as the conversion of the local resistance variations of the photo-conductive target of a vidicon into electrical signals. As has been mentioned hereinbefore, the material of the foil 9 may be polyacrylo nitrile the specific electrical resistance (,6) of which is in known manner made of the order of 10 ohm cm. at normal ambient temperature. The relative resistance variation per degree centrigrade of this foil, i.e.

1A2 pAT in the range between C. is about The diameter of the ring 10 may be, for example, 2.5 cm., and the thickness of the foil 9 may be about 1a, as mentioned hereinbefore. When the conductive layer 11 consists of gold or silver its thickness preferably is considerably less than 1,. With the aid of a tube to which the above data apply signals are obtainable on irradiation of the target screen 8 with an intensity of the order of 0.28 watt/m. irrespective of the wavelength of the infrared radiation incident on the said target screen.

At the end at which the window 2 is disposed the tube of FIGURE 1 is provided with a length of metal tubing 16 which, if required, may be in contact with a heat exchanger and by means of which the target screen 8 is maintained at an even temperature as far as possible. The said temperature may be the ambient temperature; in accordance with the nature of the material of the foil 9 it may be advantageous to maintain the target screen 8 at a higher or lower temperature.

A mosaic consisting of minute metal islands may be provided on the surface of the foil 9 facing the electron gun 3. This may be advantageous to reflect any infrared radiation not absorbed by the signal electrode 11 and the foil 9 so that a larger part of the radiation projected onto the target screen 8 is converted into heat. In addition, such a mosaic assists in the stabilisation of the surface of the foil 9 facing the gun 3 at the potential of the cathode 6 by means of the beam 7.

In order to increase the absorption of infrared radiation by the target screen 8 it may be advantageous for the foil 9 to consist not only of a temperature-sensitive polymerized material but also of a filler. When polymerized material is used which is interesting by reason of its infrared absorption spectrum but has a very high specific resistance it may be of advantage to use a filler material which is fairly conductive, for example, stannic oxide or carbon. Thus the foil 9 may be thicker than would otherwise be the case and hence will be better adapted to be handled. In general, various coloring matters may be used as fillers for ensuring an increased infrared absorp tion of the foil 9.

The absorption of the incident infrared radiation 15 need not necessarily take place in the signal electrode 11 and/or in the foil 9. The signal electrode 11 may be transparent and coated with a thin layer of material absorbing infrared radiation on the surface remote from the foil 9. This permits the selection of a material exhibiting selective absorption of the infrared radiation; if, for example, substantially long-wave infrared radiation is to be absorbed, such an auxiliary absorbing layer may consist of a silicate. Obviously the auxiliary absorbing layer must be thin enough to prevent appreciable spread ing of the generated heat in the plane of the layer.

What is claimed is:

1. In an electron discharge tube for detect-ing infra-red radiation, a target for said radiation comprising a thin layer of material having a temperature-dependent electrical resistance, a support for said layer, and an electrode carried by said support, said layer being constituted of a polymerized organic material of low thermal conductivity, said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coefficient of resistance,

p AT in the temperature range between 0 and C. of at least 5 2. In an electron discharge tube for detecting infra-red radiation, a target for said radiation comprising a thin layer of an organic thermoplastic material having a ten1- perature-dependent electrical resistance, a support for said layer, and an electrode carried by said support, said layer being constituted of a polymerized material of low thermal conductivity, said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coefiicient of resistance,

p AT in the temperature range between 0 and 100 C. of at least 5 3. In an electron discharge tube for detecting infra-red radiation, a target for said radiation comprising a thin layer of a material selected from the group consisting of polyacrylonitrile, polyvinyl acetate, and polyvinyl cyanurate and having a temperature-dependent electrical re sistance, a support for said layer, and an electrode carried by said support, said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coeflicient of resistance in the temperature range least 5%.

5. In an electron discharge tube for detecting infra-red radiation, a target for said radiation comprising a thin layer of a polychelate having a temperature-dependent electrical resistance, a support for said layer, and an electrode carried by said support said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coefficient of resistance p AT in the temperature range between and 100 C. of at least 6. In an electron discharge tube for detecting infra-red radiation, a tar-get for said radiation comprising a thin layer of material having a temperature-dependent electrical resistance, a support for said layer, and an electrode carried by said support, said layer being constituted of a polymerized organic material of low thermal conductivity and an infra-red absorptive filler material, said material having a specific resistance between and 10 ohm-cm. and a temperature coeificient of resistance p AT in the temperature range between 0 and 100 C. of at least 5%.

7. In an electron discharge tube for detecting infra-red radiation, a target for said radiation comprising a thin layer of material having a temperature-dependent electrical resistance, a support for said layer, and an electrode carried by said support, said layer being constituted of a polymerized organic material of low thermal conductivity and an infra-red absorptive conductive filler material, said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coefiicient of resistance in p AT in the temperature range between 0 and 100 C. of at least 5%.

8. In an electron discharge tube for detecting infra-red radiation, a target for said radiation comprising a thin layer of material having a temperature-dependent electrical resistance, a support for said layer, and an electrode constituted by a layer of gold or silver carried by said support, said layer being constituted of a polymerized organic material of low thermal conductivity, said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coefficient of resistance lfl p AT in the temperature range between 0 and C. of at least 5%.

9. In an electron discharge tube for detecting infra-red radiation, a target for said radiation comprising a thin layer of material having a temperature-dependent electrical resistance, a support for said layer, an electrode carried by said support, and an infra-red absorptive layer on the side of said electrode remote from said support, said layer being constituted of a polymerized organic material of low thermal conductivity, said material having a specific resistance between 10 and 10 ohm-cm. and a temperature coefficient of resistance p AT in the temperature range between 0 and 100 C. of at least 5%.

10. In an electron discharge tube for detecting infrared radiation, a target for said radiation comprising a thin layer of material having a temperature-dependent electrical resistance, a support for said layer, an electrode carried by said support, and a layer of infra-red absorptive silicate on the side of said electrode remote from said support, said layer being constituted of a polymerized organic material of low thermal conductivity, said material having a specific resistance between 10 and 10 ohmcm. and a temperature coeflicient of resistance p AT in the temperature range between 0 and 100 C. of at least 5%.

No references cited.

JAMES W. LAWRENCE, Primary Examiner. R SEGAL, Assistant Examiner, 

1. IN AN ELECTRON DISCHARGE TUBE FOR DETECTING INFRA-RED RADIATION, A TARGET FOR SAID RADIATION COMPRISING A THIN LAYER OF MATERIAL HAVING A TEMPERATURE-DEPENDENT ELECTRICAL RESISTANCE, A SUPPORT FOR SAID LAYER, AND AN ELECTRODE CARRIED BY SAID SUPPORT, SAID LAYER CONSTITUTED OF A POLYMERIZED ORGANIC MATERIAL OF LOW THERMAL CONDUCTIVITY, 